1. Field of the Invention
The present invention relates to a liquid crystal display element, a display device, and a method for driving the display device.
2. Description of Related Art
In recent years, there have been diversified demands for display devices. Display devices that can be used in various temperature environments have been demanded, for example, display devices such as car navigation systems mounted in cars and display devices mounted in airplanes.
On the other hand, a liquid crystal, utilized in a liquid crystal display device, has physical property values depending on temperature. In particular, in a low-temperature environment, the liquid crystal exhibits the property of having its viscosity increased and its response speed reduced. Thus, disadvantageously, the display quality of the liquid crystal display device such as contrast may be degraded in a low-temperature environment.
In a known method, when a liquid crystal is applied to a display device, at least two types of compounds are mixed together to increase a temperature range corresponding to a liquid crystal phase (for example, “Liquid Crystal Display”, first edition, p. 9-15, edited by the Institute of Television Engineers of Japan under the supervision of Takanori Okoshi and published by SHOKODO Co., Ltd., July 1985 (ISBN-10: 4-7856-9018-6)).
Furthermore, another means for solving the above-described problem is disclosed in JP05-173153A. Now, the structure of a liquid crystal display device disclosed in JP05-173153A will be described with reference to FIG. 34.
In a liquid crystal display element 100 in the display device described in JP05-173153A, a heater electrode layer 102b is provided on one surface of a glass substrate 101b. An insulating film 103b, a transparent electrode layer 104b, an insulating film 105b, and an orientation film 106b are provided on the other surface of the glass substrate 101b in this order. On another glass substrate 101a, a color filter 107a, an insulating film 103a, a transparent electrode layer 104a, an insulating film 105a, and an orientation film 106a are provided in this order. The glass substrate 101a and the glass substrate 101b are arranged such that the orientation film 106a is located opposite the orientation film 106b. A liquid crystal 108 is filled between the orientation film 106a and the orientation film 106b. 
The heater electrode layer is formed of a large number of rectangular electrodes disposed laterally in parallel, preferably parallel to the direction of shorter sides of the element. Furthermore, the heater electrode layer is divided into at least three independent heating areas. The rectangular electrodes in each of the heating areas are coupled together at the opposite ends of the electrodes by metal electrode terminals. Each of the rectangular electrodes forming the heater electrode layer is composed of a conductive transparent film such as ITO. The whole liquid crystal display element can be controlled to a uniform temperature by varying a voltage applied to the heater electrode layer between a central region of the liquid crystal display element and regions located at the opposite ends of the liquid crystal display element.
As described above, the display device described in JP05-173153A includes the heater incorporated in the liquid crystal display element. The display device thus allows the temperature of the liquid crystal in the liquid crystal display element (display panel) to be controlled in such a manner that the temperature is not affected by an environmental temperature.